Tubular incandescent halogen lamps include a helical filament axially mounted within a quartz lamp envelope. Filament supports attached to the filament support and center the filament within the lamp envelope. The ends of the lamp envelope are hermetically sealed, typically by press sealing. Molybdenum foil conductors electrically connect the filament through the seals to external electrical leads. The interior of the lamp envelope is typically filled with an inert gas and one or more halogen compounds.
It is important to center the filament within the lamp envelope to prevent undesired interactions between the filament and the walls of the lamp envelope. In addition, it is well known that for proper lamp performance, the spacing between coils of the filament must be precisely controlled. This is important because a slight change in filament length significantly changes the operating temperature of the filament. Any change in filament temperature will have a dramatic effect on lamp performance and life.
In one particular lamp type, filament location is even more critical. This type of lamp is known as an infrared conserving lamp, which has a wavelength selective filter coating applied to the outside surface of the lamp envelope. A central region of the lamp envelope adjacent to the filament typically has a geometrically shaped section such as ellipsoidal. The selective filter coating transmits visible radiation and reflects infrared radiation back to the filament. The reflected infrared radiation can significantly reduce the electrical power consumption of the lamp. In order to gain maximum benefit from the reflected infrared radiation, the filament must be very precisely centered on the axis of the lamp envelope. Also, in order for the filament to perform at its design temperature, the filament length must be precisely controlled.
An important component of the tubular incandescent lamp capsule described above is the filament support used to support and center each end of the filament and to conduct electrical energy to the filament. The filament supports are dimensioned to fit the inside diameter of the lamp envelope relatively closely. However, due to the large variation in the inside diameter of the lamp envelope from lamp to lamp, the filament supports must be sized a few thousandths of an inch smaller than the nominal inside diameter of the lamp envelope. It will be recognized that the lack of an intimate fit between the filament supports and the lamp envelope can result in variations in the position of the filament relative to the lamp envelope. Although the sealing process secures the molybdenum foil conductors in fixed positions relative to the lamp envelope, the filament supports may not be securely retained in the lamp envelope of the completed lamp capsule. As a result, the filament may not be positioned with the desired accuracy. Therefore, improved methods for mounting filaments in tubular double ended lamp capsules are required.
It is a general object of the present invention to provide improved tubular incandescent lamp capsules.
It another object of the present invention to provide improved methods for fabricating tubular incandescent lamp capsules.
It is a further object of the present invention to provide improved methods for mounting a filament in a tubular incandescent lamp capsule.
It is yet another object of the present invention to provide methods for accurately positioning a filament within a tubular lamp capsule.
It is still another object of the present invention to provide methods for mounting a filament in a tubular incandescent lamp capsule which are low in cost.